As of the census[2] of 2010, there were 3,532 people, 1,439 households, and 868 families residing in the city. The population density was 1,385.1 inhabitants per square mile (534.8/km2). There were 1,663 housing units at an average density of 652.2 per square mile (251.8/km2). The racial makeup of the city was 94.6% White, 0.4% African American, 1.6% Native American, 0.3% Asian, 0.1% Pacific Islander, 1.0% from other races, and 2.0% from two or more races. Hispanic or Latino of any race were 3.4% of the population.

There were 1,439 households of which 27.2% had children under the age of 18 living with them, 47.0% were married couples living together, 8.9% had a female householder with no husband present, 4.4% had a male householder with no wife present, and 39.7% were non-families. 34.7% of all households were made up of individuals and 13.3% had someone living alone who was 65 years of age or older. The average household size was 2.24 and the average family size was 2.86.

The median age in the city was 39.6 years. 22% of residents were under the age of 18; 8.9% were between the ages of 18 and 24; 25.7% were from 25 to 44; 27.2% were from 45 to 64; and 16.2% were 65 years of age or older. The gender makeup of the city was 53.9% male and 46.1% female.

As of the census[4] of 2000, there were 3,065 people, 1,253 households, and 844 families residing in the city. The population density was 1,242.1 people per square mile (479.1/km²). There were 1,458 housing units at an average density of 590.9 per square mile (227.9/km²). The racial makeup of the city was 95.79% White, 0.13% African American, 1.44% Native American, 0.29% Asian, 1.01% from other races, and 1.34% from two or more races. Hispanic or Latino of any race were 1.66% of the population.

There were 1,253 households out of which 30.4% had children under the age of 18 living with them, 54.0% were married couples living together, 10.1% had a female householder with no husband present, and 32.6% were non-families. 28.4% of all households were made up of individuals and 13.0% had someone living alone who was 65 years of age or older. The average household size was 2.35 and the average family size was 2.88.

In the city, the population was spread out with 24.3% under the age of 18, 7.9% from 18 to 24, 24.7% from 25 to 44, 24.5% from 45 to 64, and 18.6% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 93.1 males. For every 100 females age 18 and over, there were 91.5 males.

The median income for a household in the city was $29,873, and the median income for a family was $36,929. Males had a median income of $31,222 versus $16,628 for females. The per capita income for the city was $15,378. About 7.5% of families and 11.4% of the population and 7.5% of families were below the poverty line, including 14.8% of those under the age of 18 and 15.7% of those 65 and older.

Public education in the city of Newcastle is provided by Weston County School District #1. The district's schools include Newcastle Elementary (split into two campuses for grades K-2 & 3-5), Newcastle Middle School (grades 6-8), and Newcastle High School (grades 9-12).

The town boasts great walking trails. A historic tour starts at the Anna Miller Museum. Also included are the Greenwood Cemetery and a downtown historic district listed with the National Register of Historic Places. The "Serenity Trail" allows walkers to view wildlife in the area.

Kody Templeman, Cory Laurence, and Zachary Rawhouser were all members of the band The Lillingtons, who released four albums, including two on influential punk rock label Lookout! Records. All three are Newcastle residents. Templeman also currently co-fronts Fat Wreck Chords recording artists Teenage Bottlerocket, along with fellow members from Laramie, Wyoming.

Koree Khonghpand-Buckman, Founder of Underwearness Inc. It is a nonprofit that provides new underwear to children who need it.

Hans Hunt, Member of the Wyoming House of Representatives, currently the Majority Whip, was born and raised in Newcastle. He was elected to the House of Representatives in 2010 at the age of 24.